The present invention relates to a method and a device for manufacturing laminated plate material, such as are widely used as electrical insulation material and so forth, and in particular relates to such a method and device for producing laminated plate material, in which the pressure applied to the laminate is made to be more constant and uniform over the whole area of the laminated plate material.
Conventionally, laminated plate materials such as synthetic resin laminates are manufactured by: (1) impregnating a base material such as paper or glass cloth with phenol resin, epoxy resin, polyimide resin, or the like; (2) drying this material to form the so called "prepreg" material (this abbreviation, which will be used henceforward in this specification, stands for "pre-impregnated material"); (3) stacking up a number of prepregs into a stack of the required thickness for the final laminated plate material, including if required one or two outer surface layers of copper foil or the like on one or both of the outer surfaces of the stack to be laminated together with it; (4) placing this stack assembly in between two mirror plates made of for example stainless steel of thickness 1 to 3 mm, so as to form a completed sandwich assembly; (5) inserting the resulting sandwich assembly in between two end plates of a multi opening press machine for laminating; (6) squeezing the two end plates together so as to pressurize the sandwich assembly; and (7) heating up the sandwich assembly and maintaining the heat and pressure conditions on the compressed and heated stack for a certain appropriate time period. One or more cushion plates are often interposed between one of the end plates, or both of them, and the sandwich assembly, in order to provide an even pressure distribution over the entire surface of the laminated material, and in order to ensure an even temperature distribution. Further, in order to make best utilization of the large and expensive mechanism of the press, it is usual to in fact insert a large number of such sandwich assemblies in between the two end plates of the press, further including other intermediate plates and cushion plates in the superposed stack; and the pressure exerted by the press is transmitted through the entire stack. In this case, it is usual that the intermediate plates are formed as hot plates each incorporating heating means therein.
This type of prior art laminating process is shown in schematic sectional view in FIGS. 1 and 2 of the accompanying drawings. FIG. 1 shows a section through a stack consisting of a number of sandwiches of prepregs 1 and mirror plates 2, which is being supported on a carrier plate 4 with a cushion plate 3 interposed between the carrier plate 4 and the proximate mirror plate 2 in order to make for a more even pressure distribution. Further, FIG. 2 shows a side view partly in section of a press 8 charged with a number of such stacks as shown in FIG. 1 as carried on the carrier plate 4: in this figure, the press 20 comprises a base 8 which is formed with a cylinder in which a piston member 9 slides, and the cylinder chamber 10 defined under the piston 9 in the figure selectively either is supplied with pressurized hydraulic fluid from a hydraulic fluid reservior 11 by a pump 13 or is exhausted of hydraulic fluid through a valve 12 to said reservoir 11. Thereby the piston 9 is selectively either forced in the upwards direction in the figure or is lowered therein. Further, on the top of the piston 9 there is fixed a lower end plate 7, which can slide upwards and downwards, as the piston 9 is raised or lowered, along slide guide members 6, 6 which are fixedly mounted on the base 8. To the top of the slide guide members 6, 6 there is fixedly mounted an upper end plate 5, and accordingly when the piston 9 is raised by supply of hydraulic fluid to the chamber 10 by the pump 13 then the upper and lower end plates 5 and 7 are brought towards one another with a very high pressing force, while on the other hand when the piston 9 is lowered by draining of hydraulic fluid from the chamber 10 through the valve 12 then the upper and lower end plates 5 and 7 are brought apart from one another. And between the upper and lower end plates 5 and 7 there are placed a number of stacks like the stack of FIG. 1, each consisting of a number of prepregs 1 and mirror plates 2 stacked together and supported on the lower end plate 7 and the intermediate plates 14 with a cushion plate 3 interposed between the supporting plate member 4 and the proximate mirror plate 2. The intermediate plates 14, which are generally formed as hot plates as described above, are slidingly mounted on the slide guide members 6, 6. The slide guide members 6, 6' are provided, through this is not shown in the figure, with stop means spaced therealong which are adapted to hold the intermediate plates 14 from sliding down beyond certain predetermined level positions, so that the intermediate plates 14 are held as spaced from each other when the lower end plate is lowered to its lowermost position for the convenience of loading and unloading of the stacks of prepregs into and out of the spaces defined between the upper and lower end plates 5, 7 and the intermediate plates 14.
In operation, each stack of prepregs 1 sandwiched between the mirror plates 2 is carried on the carrier plate 4 as shown in FIG. 1, is charged into each space defined between the upper and lower end plate 5, 7 and the intermediate plates 14, and is placed on the lower end plate 7 or on one of the intermediate plates 14, with the carrier plate 4 being removed thereafter. Then fluid pressure is supplied to the cylinder chamber 10 to drive the piston 9 upwards to pressurize the whole set of stacks of prepregs together, with interposition of the intermediate plates 14.
However, this prior art type method for manufacture of a laminated material, and device for performing such manufacture, are prone to the following problems.
First, because the cushion plate 3, which is provided in order to ensure even temperature and more particularly pressure during the lamination, is typically made of paper or rubber or the like, it suffers fatigue because of heat and pressure degradation and because of scuffing from the edges of the mirror plates 2, and its life is limited to at most 500 cycles.
Further, especially later in the life of such a cushion plate 3, its thickness may become uneven, and this can lead to unevennesses in the pressure distribution over the materials which are being laminated, thus possibly leading to defects in the finished laminated material. In any case, even when the cushion plate 3 is relatively new, its function for distributing the pressure applied to the sheets to be laminated uniformly over their entire surface area is not completely effective, and poor pressure distribution inevitably occurs.
Also, because the cushion plates 3 are used, the thermal transmission between the hot plate type intermediate plates 14 and the material to be laminated is reduced, and this means that the speed of the laminating process is low.
Finally, a particularly troublesome problem relates to the distribution of the pressure applied by the squeezing together of the top and bottom end plates 5 and 7. Since inevitably some friction arises between the intermediate plates 14 and the slide guide members 6, 6 (and this friction can become quite severe in the case of some skewing of the stack, even slight skewing), and since moreover sticking between one of the intermediate plates 14 and one of the slide guide members 6 can arise, there is a danger that one of the stacks of prepregs 1 and mirror plates 2 may be compressed more than another. This can further lower the quality and uniformity of the finished laminate produced as described above.